Cargo theft and intentional damage to cargo carried on rail, shipping and air lines is steadily on the rise with cargo industry estimates of loss from cargo in transit and storage surpassing the $30-$50 billion per year. In order to protect cargo in transit or storage, it is known to provide cargo seals on the entrance of cargo containers as part of good security practice. The principal purpose of a cargo seal is to assure carriers, beneficial owners of cargo, and government officials that the integrity of a shipment is intact by acting as a ‘tell-tale’ indicator that a cargo container has or has not been tampered with. There are two major categories of cargo container seals, i.e., indicative and barrier seals, both of which detect tampering or entry.
Indicative seals are usually made of plastic, wire, or strips of sheet metal marked with a unique serial number or identifier. These seals may be looped through a hasp or around locking bars and handles so that the container or trailer door cannot be opened without removing the seal. Indicative seals offer no physical protection, they simply reflect whether or not the sealed entrance has been compromised. They may be used together with locks or alone.
Barrier seals add physical protection to tamper detection and are more difficult to defeat. It usually takes bolt cutters or special tools to remove a barrier seal, not simple wire cutters or a sharp knife. Barrier seals take many forms, with the simplest using steel cable rather than wire. Bolt seals are generally more protective, using heavy-duty bolts with specialized single-use locking nuts and unique identifiers.
Barrier seals vary widely in the degree of protection they offer. Many factors affect protection, including the design, materials, and construction of the locking device, and the design and materials in the hasp, bolt, or cable. However, the typically robust appearance of such seals does not guarantee great protection as they can be defeated by experienced and determined criminals. Further, the trade abounds with tales of popular barrier seal designs that have been copied with inferior materials.
Electronic seals can simply mirror the traditional indicative and barrier seals in terms of protection. Some approaches use electronics as intrusion sensors or indicative seals. It is also common to find electronic devices married to traditional barrier seal components such as steel bolts and cables.
More sophisticated and expensive approaches use electronics to control the operation of locks and seals. One approach programs a latitude/longitude location or key code into the seal, which will not open until an internal or external device confirms the correct location or code. Another approach enables remote control of the locking mechanism via satellite or radio frequency (RF) messages.
Still another approach uses electronic seals that have sensors equipped with radio frequency transponders that generate radio frequency signals that indicate that a mechanical door seal has been tampered with. In some cases, the transponders provide self-identifying signals. Radio frequency transponders of this latter type are commonly known as Radio Frequency Identification (RFID) tags. There are two main types of RFID tags, passive and active. Passive tags do not initiate transmissions, i.e., they respond when activated by the energy in the signal from a reader. Interrogated by a reader, a passive tag can identify itself by reporting its identification number, analogous to a standard bar code. The passive tag can also perform processes, such as testing the integrity of a seal. One advantage of a battery-free passive seal is that it can be a simple, inexpensive, and disposable device. Although not a formal term, it is useful to think of such devices as purely “passive” a term that describes what most have in mind when they discuss passive RFID electronic seals.
However, passive RFID seals can carry batteries for either or both of two purposes. The first is to aid communication by boosting the strength of the reflective signal back to the reader. The second purpose is to provide power so functions can be performed out of the range of readers. One example of the latter is to power a clock, so that the integrity of the seal can be periodically tested and, when the integrity is compromised, a record can be made indicating the time that the seal was tampered with. Adding substantial capability, however, could raise the cost of a passive seal sufficiently that it would be practical only as a reusable product.
Conventionally, users employ three different terms to describe passive tags with batteries. They are semi-active, semi-passive, and battery-assisted passive. Since the terms appear to be used in the art in an interchangeable manner, this is a source of confusion in RFID tag discussions. Some manufacturers have used the term semi-passive, but are now transitioning to the term battery-assisted passive to reduce customer confusion.
Besides the battery-assisted passive RFID tag, all other known passive electronic seals are “pure passive,” with no battery whatsoever. Pure passive functionality is limited to testing the integrity of the seal when interrogated by a reader and reporting that status, its ID, and other on-board information to the reader. Further, manual seal manufacturers often use batteries on passive tags, preferring instead, if forced to use a battery in the tag doing so in the context of an active seal.
Passive seals tend to be short range and directional to maximize antenna exposure to reader signal strength. Maximum read range for electronic seals without battery-assisted communications tends to be two or three meters, with some debate about efficacy beyond two meters. Adding a battery can boost the range, i.e., design target is greater than 30 meters, but concerns about safety, regulations, and the operating environment impose practical limits on power and range.
Active seals can initiate transmissions as well as respond to interrogation. All active tags and seals require on-board power, which generally has meant providing the tag with some sort of a battery.
A major attraction of active tags and seals is the potential for longer-range and omni-directional communications, i.e., up to 100 meters. Customers expressed need for greater range and the ability of signals to wrap around obstructions in terminal operating environments prompted an international standards group working on electronic seal and read/write container RFID standards to add active RFID protocol(s).
At the lowest functionality, active seals typically cost more than pure passive seals because of the battery and the ability to initiate communications, but the difference would be relatively small. Actual price differences between passive and active RFID seals in the marketplace tend to be much larger, reflecting design choices to host greater functionality on active tags, i.e., taking advantage of the battery, the potential to initiate communications, and the greater, more flexible range.
All active RFID electronic seals in or approaching commercial use monitor seal integrity on a near-continuous basis, and most capture the time of tampering and write it to an on-board log. Examples of such seals are shown in U.S. Pat. No. 5,831,531 (Tuttle), U.S. Pat. No. 6,501,390 (Chainer et al), U.S. Pat. No. 6,069,563 (Kadner et al) and U.S. Pat. No. 5,117,222 (McCurdy et al) each of which are hereby incorporated by reference and are directed to an RF tag provided with a battery for detecting and actively (or passively) reporting to a unit, e.g., interrogator attached to a host computer. Some RFID seals can accept GPS and sensor inputs, and some can provide live “mayday” tampering reports as the events happen, mostly within specially equipped terminals.
There are trade-offs between these technologies from theoretical and practical perspectives. Theoretically, the only difference between passive and active tags and seals is the ability to initiate communications from the tag—a distinction that means, for example, that passive RFID tags could not initiate mayday calls or generate routine self-initiated status signals.
However, there is an unmistakable clustering in the marketplace, in which an overwhelming number of manufacturers choose cost and simplicity, i.e., passive RFID-based seal designs which are battery-free.
The types of cargo seals described above are placed on the entrance to a cargo container and as a result many thieves simply avoid these conventional cargo seals by simply cutting through a roof, side wall or bottom of a cargo container to avoid the seal altogether. There is a distinctive need for a low cost, easy to install cargo seal which is reliable and cannot be defeated by simply avoiding the seal altogether.
All of the above are used for protection or detection of tampering at the entrance, door or opening of a container and do not address tampering of the sides of a container.